My servo I can tune down the max speed to fairly slow, it adjusts in 100rpm increments and I tend to sew mostly 600-800, if lots of straight lines I can go faster but typically the 600/800 area works well. The pedal varies the speed too in addition up to the maximum setting. I don’t use the ramp up feature on mine just max speed and foot position. The needle position is a sensor on the sewing machine shaft telling the unit where top dead center and bottom dead center are so depending on what you pick when you let off the foot it finishes a stitch in the chosen position. I used needle down so I can easily pivot stuff around. If I push in the heel side of the pedal it jumps to top dead center to free up what I am sewing from the machine.
Maybe you need different ratio pulleys to slow yours down more?
Maybe you need different ratio pulleys to slow yours down more?